Sealing of horizontally-split centrifugal compressors



United States Patent 3,384,296 SEALING 0F HORIZONTALLY-SPLIT CENTRIFUGALCOMPRESSORS Wilhelm Kahane, The Francouia, 20 W. 72nd St., New York,N-Y. 10023 Continuation-impart of application Ser. No. 630,933, Apr. 14,1967. This application May 19, 1967, Ser. No. 639,764

1 Claim. (Cl. 230-133) ABSTRACT OF THE DISCLOSURE A sealing is describedfor horizontally-split casings of centrifugal compressors. The interfaceof the flanged joint of the casing contains injection grooves into whicha seal-liquid is injected under a pressure higher than that of thecompressed gas. Said interface also contains drain grooves runningbetween said injection grooves and its outer contour to prevent lossesof the seal-liquid across the joint. Both sets of grooves are connectedto the hydraulic-type shaft-sealing system of the compressor. Theinjection grooves communicate with the high pressure end of theshaft-sealing system and, being filled with seal liquid under a pressurein excess of that of the compressor pressure chamber, constitute apositive barrier against gas leakages. The drain grooves communicatewith the low pressure end of that shaft-sealing system and preventescape of seal-liquid from the interface into the atmosphere around thecasing.

Horizontally-split casings, provided with this sealing,

can be allowed the same maximum working pressure in the compression ofhighly hazardous hydrogen-rich gases as in the compression of air.

This invention is a continuation-in-part of that which was disclosed inmy application Ser. No. 630,933 of Apr. 14, 1967, concerning the sealingagainst gas leakages through the joint made by the two flange-boltedhalves of the casing of horizontally-split centrifugal compressors. Thepresent invention consists in the provision of the interface of thatjoint with a groove system that receives a seal liquid under a pressurethat is higher than that of the discharge pressure of the gas beingcompressed, said liquid and its pressure being taken from the shaftsealing system. That grooving system contains two channels that act asbarriers, one against the entrance of gas leaks from the compressorspressure chamber into the joint, the other one against the entrance ofseal liquid leakages from the joint into the ambient atmosphere aroundthe compressor.

FIG. 1 is an elevational schematic, partly sectional view of ahorizontally-split centrifugal compressor provided with the inventeddevice.

FIG. 2 is a plan view of one of the two halves of the compressor casing,showing the interface of the joint made by the two flange-bolted halvesof that casing.

FIG. 3 is an enlarged cut-away plan view of the interface shown in FIG.2, and represents an alternate arrangement of the grooves.

FIG. 4 is a cross-sectional view of the compressor casing along thevertical plan 4-4 of FIG. 1.

In horizontally-split casings, comprising a flangebolted joint andhandling toxic, or highly hazardous, or low molecular weight gases, themaximum admissible working pressure is controlled by the maximumacceptable rate of gas leakages through the joint into the ambientatmosphere around the compressor rather than by the wall strength of thevessel. This is why one and the same horizontally-split centrifugalcompressor casing which, as an example, is rated at 800 p.s.i. when usedin 3,384,296 Patented May 21, 1968 the compression of air, cannot bepermitted more than 300 p.s.i. if the gas to be compressed contains animportant amount of hydrogen. This is so because hydrogen presents agreat fire and explosion hazard and because, due to its low molecularweight, it has a high diffusivity through the sealing imperfections ofthe joint. In the above example where, in the present status of the art,hydrogen-rich gases are to be compressed at 800 p.s.i. in ahorizontally-split casing, the above mentioned loss in the casingsmaximum working pressure has the following unfavorable consequences.First, the compression of hydrogen-rich gases at 800 p.s.i. can nolonger be done in the large size (inside diameter) casings that wereadmissible for the compression of air, but only in smaller size ones,whose basic much higher maximum Working pressure for air was high enoughto still withstand 800 p.s.i. when compressing hydrogen-rich gases.Therefore, in the present status of the art, instead of using one singlehigh-capacity unit compressor manufacturers are compelled, in theconditions of that example, to connect in parallel two or more units ofa smaller size. The drawbacks of this arrangement are a higher occupiedfloor space and higher investment costs. Besides, for any givencompressor type, the smaller the size (inside diameter) the lower thehydraulic efficiency of the compression and the higher the horsepowerconsumption. Permanent tightness of the joint is more difficult toachieve in horizontally-split than in verticallysplit barrel typecentrifugal compressors, because of the pressure and temperatureincreasing along the joint from the suction to the discharge end, andbecause the temperature and pressure departures in time from the normalmay vary greatly along that joint. This is why, in the compression ofhydrogen-rich or other low molecular weight gases, vertically-splitcompressors have replaced the horizontally-split ones despite a muchhigher cost, lower maximum capacities (with the result of a lowerhydraulic efficiency and a higher consumption of power) and a largeroccupied floor space.

All attempts done in the past to increase the permanence of thetightness of the joint of horizontallysplit casings by means of gasketshave proved unsuccessful and even dangerous. so that now only ametal-tometal contact is acceptable in the joint of the two halves of ahorizontally-split centrifugal compressor casing. I concluded that, inorder to eliminate hazards while still being able to use, in thecompression of hydrogen-rich or other dangerous gases, the same largesize casings at their full maximum working pressure as in thecompression of air, a fluid over-pressure or under-pressure barrier forleakages is needed in the joint. Such a barrier can be created by usinghydrodynamic means existing in the shaft-sealing system of thecompressor. In the invention disclosed with my application Ser. No.630,933, I proposed as a solution to that problem the under-pressurebarrier resulting from the slight vacuum created in a vent channel ofthe joint in communication with the compressors bearing isolationchambers, that are a part of the shaft-sealing system and are kept undera slight vacuum. The fluid pressure barrier proposed in the presentspecification is that of a seal liquid injected into a groove, in theinterface of the joint, at a pressure in excess of the dischargepressure of the gas being compressed. A distinctive feature of theinvention is that the seal liquid and its pressure are taken from theshaftsealing system of the compressor. Another feature is the provisionof a second barrier, this latter one for the prevention of seal liquidleakages to the atmosphere around the casing.

Injection of a seal liquid in the interface of joints has been used inother pressure vessels but never before in the joint ofhorizontally-split casings of centrifugal como pressors, in spite thatsuch a use, as described in the present specification, would have sincelong solved the problem of boosting the maximum working pressure oflarge size horizontally-split compressors, when compressing hazardouslow molecular weight gases, up to that which is admissible in thecompression of air. The stringency of that problem, which is more than30 years old, resulted from the ever increasing proportion ofcompressors for hydrogen-rich gases (used in the synthesis of ammoniafor fertilizers, in that of gaseous compounds for the plastics industry,and for the upgrading of lubricating oils and other crude oil fractionsthrough hydrogenation) as compared to those handling other gases. Whatgives practical value to this invention is the combination of theinjection of a seal liquid in the casings joint with the use of meansalready existing in the shaf sealing system of the compressor.

Most present centrifugal compressors, no matter whether horizontallyorvertically-split, that handle dangerous or low molecular weight gases,are provided with a hydraulic-type shaft-sealing system. The liquidordinarily employed in these sealings is either lubricating oil orwater. Other liquids are used when the quality of the gas or that of theseal liquid might be impaired through their contact under pressure. Atypical hydraulic shaftsealing system, currently used today incentrifugal compressors handling toxic or hazardous or low molecularweight gases, comprises the following items represented schematically inFIG. 1, which is an elevational schematic, partly sectional, view of ahorizontally-split centrifugal compressor provided with the inventeddevice. A reservoir 1 for the circulation of the seal liquid containsthe suction pipes of the main seal pump 2a and auxiliary seal pump 21).They use two different kinds of motive power and are automaticallyswitchable. The seal liquid is pumped through interchangeable filters 3aand 3b, cooler 30 and overhead seal liquid tank 5 to the injection lines6a and 6b into the compressors shaft-seals 7a and 7b.Differential-pressure regulators 8a and 8b, actuated respectively by thegas suction and discharge pressures, maintain in the injection lines 6aand 6b a constant excess pressure over the gas pressure in the spaces 9aand 9b of the gas pressure chambers adjacent to the shaft-seals 7a and7b. To this effect the regulator 8a, that controls the injection intothe line 6a to the shaft-seal 7a that is located at the gas suction endof the compressor, is connected to the compressors gas suction throughline 100; while the regulator 817, that controls the seal liquidpressure in the injection line 611 to the shaft-seal 712 that is locatedat the gas discharge end of the compressor, is actuated by thecompressors discharge pressure through line 1012. Positive shaft-sealing is accomplished following the injection of seal liquid between twostationary floating rings 11 at a pressure slightly above that of thegas in the pressure chambers 9a and 9b to be sealed. The excess pressureof the seal liquid over that of the gas prevents gas leakage past sealrings 11. Seal liquid flows between the sealing rings 11 and the shaft12, both toward the gas pressure chambers 9a and 9b and then back to thepump through the internal drains 13, which comprise gas separators 14,and toward the shaft bearings 15 and then back to the pump through theexternal drains 16. Both seal leakages, that which goes into the gasstreams of chambers 9a and 9b as well as that which flows toward theshaft-bearings 15 in contact with the atmosphere 17, are minimizedordinarily by dry seals of the labyrinth type, not shown. The sealliquid, which is recovered through the drains 13 and 16, is returned tothe reservoir 1 and recirculated indefinitely. The losses through theseals are very small and occur mostly into the gas stream. When the sealliquid used is lubricating oil, the oil from drain 16 is used quiteoften to lubricate the shaft bearings 15. In most applications, theabove described hydraulic shaftsealing system is built in a console asan aggregate together with the necessary automatic switches for pumpsand controls, including those for positive sealing during shut-downperiods.

FIG. 2 is a plan view of one of the two halves of the compressor casing,showing the interface 18 of the joint made by the two flange-boltedhalves 19 and 20 of the compressor shown in FIG. 1. For a bettercomprehensible description, the example considered in FIGS. 1 and 2 isthat of a compressor with two open shaft ends.

The present invention consists in the provision of the horizontalinterface 18 of the joint, made by the two flange-bolted halves 19 and20 of horizontally-split casings for centrifugal compressors, with agroove system consisting of narrow channels 21 and 22 in that interface,cut in the metal of one of said halves. These channels act as positivebarriers against leakages. Their general direction is that of thecenter-line of the row of boltholes 23. The injection channels 21 run insaid interface between its inner edge 24, that bordering with thecompressors pressure room 26, and the row of bolt-holes 23, at a safedistance from both. These injection channels 21 are connected, by meansof two lines 25, to the previously mentioned injection line 6b, thatsupplies with seal liquid that shaft-seal 7b, which is located at thegas discharge end of the compressor. Said supply of seal liquid is doneunder the pressure existing in line 6b, which exceeds the gas dischargepressure by a constant amount as controlled by the previously mentioneddifferential-pressure regulator Sb. The seal liquid injected intochannel 21 is either stationary or, if so desired in order to avoidclogging of that channel, under a very slight motion. Its pressure, allalong its length, being higher than that of the gas in any point of thecompressors pressure room 26, no gas from that room can leak into theinterface of the joint toward channel 21 and then further to the ambientatmosphere 17 around the compressor. it follows therefore that saidinjection channel 21 forms an over-pressure barrier against the entranceof gas from the compressors pressure room into the interface of thecasings joint.

But, because of the high pressure of the seal liquid in the injectionchannel 21, the imperfections of the metal-t0'metal sealing of the jointmay cause minute leakages of seal liquid from channel 21 across theoutside contour 27 of said interface or through the clearance space 33along the bolts in bolt-holes 23 to the ambient atmosphere 17 around thecompressor. For this reason the system of grooves of the interface 18includes drain channels 22, whose general direction is the same as thatof the injection channels 21, namely that of the row of bolts 23. Thesedrain channels 22 are located between the injection channels 21 and theouter contour 27 of the interface. As to the position of channels 21 and22 with regard to the row of bolt-holes 23, it is to be noted that thedrain channels 22 may run either between an injection channel 21 and therow of bolt-holes, as shown in the example represented in FIG. 2, or, asin the alternate grooving arrangement represented in FIG. 3, it mayintersect the bolt-holes. But no bolt-hole is permitted between aninjection channel 21 and a drain channel 22, unless intersected by thelatter. The drain channels 22 are connected by means of lines 28 to theseal liquid drain line of the previously described hydraulicshaft-sealing system. The path of any possible drop of seal liquid thatmight leak from an injection channel 21 toward the ambient atmosphere 17around the compressor, either directly through the outer contour 27 ofthe interface 18 or via a bolt-hole, would be barred by a drainingchannel 22. Thus no seal liquid can be lost to the atmosphere. Itfollows that said drain grooves might be viewed as forming anunder-pressure barrier (as the suction pressure of the pumps is ingeneral lower than the atmospheric pressure) against the entrance ofseal liquid leakages from the injection grooves of the interface intothe ambient atmosphere. FIG. 4 is a cross-sectional view through thecasing joint along a vertical plan marked 44 in FIG. 1. It shows thepositions of the injection channel 21 and drain channel 22 when thelatter runs between the injection channel and the row of bolt-holes 23,as in the alternate represented in FIG. 2.

In present horizontally-split compressor casings, a very slightimperfection in the tightness of the joint may cause a dangerous loss ofgas, the more so when that gas contains an impontant amount of hydrogen.But, because the motion of liquids through leaks is incomparably morerestricted than that of gases, that slight imperfection would cause, incasings protected by the invented device, at the very most only a verysmall loss of seal liquid into the gas stream and no loss at all to theatmosphere. That loss into the gas stream will be by far smaller thanthat which now flows into the gas stream from around the shaft in thebest possible shaft-seal because, while the stationary and the movingparts of the latter can be pressed together only gently, the two halvesof the casing are pressed together very strongly by bolts.

The invented casing seal adds practically no power load and noadditional investment in auxiliary equipment to those of the alreadyexisting shaft-seal system of the compressor.

In order to prevent a possible clogging of channels 21 and 22 for lackof circulation therein, by-pass lines 29 and 30, provided with valves,might be added. In normal operation, valve 31 on by-pass 29, thatshort-circuits an injection channel 21 to the drain of the shaft-sealsystem to reservoir 1, is closed. It may be opened slightly for shortperiods of time to prevent deposition of clogging material in channel21. In normal operation, also valve 32 on by-pass line 30, that allows apositive fiow of seal liquid through drain channel 22 to its drain line28, is closed, but may be opened slightly for short periods of time toprevent deposition of clogging materials in channel 22.

Summing up, the invented device is a combination of the following threeelements: (1) a flange-bolted, horizontally-split casing for centrifugalcompressors; (2) a system of grooves in its joint; and (3) theconnection of that system of grooves to the shaft-sealing system of thecompressor. When provided with this device, horizontallysplitcentrifugal compressors acquire the same maximum admissible workingpressure for the compression of hydrogen-rich gases as for thecompression of air. Its application in large-capacity compression plantsfor hydrogenrich gases frees the user from the need, that exists in thepresent status of the art, of employing either a larger number ofsmaller units, instead of a single large horizontally-split unit, oremploying a vertically-split barrel type compressor, both presentalternatives imposing an unnecessary increase in capital investment andconsumption of power. Because of that combination of elements, thisresult has been obtained without introducing any complication and cost,by simply connecting the casing-sealing system to the existingshaft-sealing one.

What I claim as new is:

1. In a centrifugal compressor provided with a hydraulic shaft-sealingsystem, operated with a seal liquid that is recirculated by a pumpbetween its high-pressure end, which is connected to the discharge ofthat pump, and whose pressure is in excess of the gas dischargepressure, and the low pressure end of that shaft-sealing system, whichis connected to the suction end of the pump;

a horizontally-split casing made of two flange-bolted halves pressedtogether by a row of bolts against the interface of the mutualmetal-to-metal contact of the joint of said two halves, in combinationwith:

(a) seal liquid injection grooves, in that interface, with their generaldirection following that of the row of bolts, said injection groovescontaining seal liquid under a pressure in excess of the gas dischargepressure; said injection grooves being located between the bolt holesand the inner contour of said interface; the injection grooves thusforming an over-pressure barrier against the entrance of gas from thepressure chamber of the compressor into the interface of the casingjoint;

(b) seal liquid drain grooves in said interface, with their generaldirection following that of the row of bolts, and leading outside ofsaid interface, where they drain the leakages coming into them from theabove described injection grooves; these drain grooves being locatedbetween said injection grooves and the outer contour of the interface;said drain grooves thus forming a barrier against the entrance of sealliquid leakages from the above described injection grooves of theinterface into the atmosphere around the casing;

(c) communications between the seal-liquid injection grooves and thehigh-pressure end of the hydraulic shaft-sealing system of thecompressor, whereby said injection grooves receive from thatshaft-sealing system seal liquid under the above mentioned pressure inexcess of the gas discharge pressure of the compressor;

(d) communications between the seal-liquid drain grooves and the lowpressure end of the hydraulic shaft-sealing system of the compressor,whereby said drain grooves drain into that shaftsealing system theleakages of seal-liquid escaped from the injection grooves into them.

References Cited UNITED STATES PATENTS 1,058,936 4/1913 Bancel 253--391,607,234 11/1926 Brown 230-205 2,590,803 3/1952 Unger et al 220--463,055,538 9/1962 Schoessow 22046 3,144,035 8/1964 Hablanian et a1 277-1HENRY F. RADUAZO, Primary Examiner.

